The plants and animals that make their homes in Riveredge Nature Center in the Town of Saukville, responding to ever longer days, are saying spring is pretty much here. We’ll know for sure when the big snapping turtle comes out of hibernation and makes a menacing appearance.

It seems everyone has spring fever luring them outdoors to work, play or search for signs of nature reawakening. Spring is earlier this year, some say, as they spot a robin, hear birds warbling or push away old leaves to reveal daffodils and tulips sprouting.

It may seem earlier, but everything is pretty much on schedule, said Mary Holleback, research and stewardship educator at Riveredge Nature Center in the Town of Saukville.

“It’s almost amazing how the same bird (species) will come back every year on the same day,” Holleback said. “It’s not warm weather, but the length of day that triggers birds to start migrating. It’s their genetics.

“The first southern robin came back Feb. 21. During the Christmas bird count, I counted 150 robins, but they were northern robins.

“Sometimes, it’s just a matter of us not being out there to see them. It’s been a nice week so that’s why people are noticing things.”

A yellow rump warbler and golden crowned kinglet have been spotted at Riveredge, she said.

Holleback, who has a master’s degree in education and undergraduate degrees in biology and conservation, keeps a record of what she sees or hears each day, paying particular attention to the “firsts” of each season.

She started volunteering at Riveredge when her children were toddlers, became a volunteer teacher naturalist in 1984 and a full-time educator five years ago, so her notes encompass more than 25 years.

During a hike last week, Holleback pointed out signs of spring that are appearing or disappearing daily in the ponds, forests, wetlands and prairies.

The first bluebird was seen last week. The male’s bright color seems to bring a smile to everyone’s face, said Holleback, who started the center’s bluebird trail.

While volunteers were cleaning the 40 boxes, a bluebird perched on one, right on schedule, Holleback said.

“I tell people they can remember the bluebirds by the holidays. St. Patrick’s Day, they come back. By Easter, they have a nest and lay eggs, and by Mother’s Day the babies are big enough to fledge,” Holleback said.

The male comes first, scouts out the territory and picks four or five boxes. When the female comes, the male shows her all the nesting spots. It’s the female who picks the spot and her mate, Holleback said.

If a sparrow attempts to nest in a box, volunteers will cover the hole for a week.

“Sometimes, we let them nest in one to keep them from going to another box,” Holleback said. “We keep removing their eggs so they don’t reproduce.”

Ice covered about half of the two ponds closest to the center last Friday, but by Monday, the ice had almost disappeared.

On the first pond, a pair of giant Canada geese swam together. They will build a nest on the pond’s island.

The migrating pair have returned for several years, Holleback said. Local geese usually don’t stop at Riveredge, she said, because the vegetation, which can get very tall, is not cut around the ponds.

“We’re fortunate that we only have one pair. This pair came back even before the ice started to melt,” Holleback said. “As with other species, most do go back to the area where they successfully raised a brood.

“They have nested on the far side of the island every year. We’ll have students walking around the pond, and they will sit tight on the nest no matter how many kids are there.

“After the young are older, they’ll walk across the street and spend most of the time on the river, which is safer for them.”

The geese probably chose the island because raccoons and foxes can’t get to it, Holleback said.

“But they’ll have to deal with a huge snapping turtle in the pond. We’ll be seeing it sometime soon,” she said. “Water temperatures influence when the turtles come out of hibernation.”

That is also true of frogs and toads, with each species emerging at different temperatures, Holleback said.

Although she hasn’t heard one yet, volunteer Kate Redmond heard her first spring peeper last week.“It was probably in a shallow ditch. Our ponds are deeper and it will take a little while for them to warm up. We won’t hear them until the water temperatures get to 45 to 50 degrees,” she said.

“The wood frog, which several people spotted, is the earliest caller, then the peeper, leopard and tree frogs. The American toad is the last in May.”

Juncos, which flocked to bird feeders during the winter, haven’t been seen for several weeks, she said.

Male goldfinches, which lose their bright colors in winter, are starting to sport a little yellow and soon should have their full cheerful plumage. The females are an olive color with pale yellow breast.

Chickadees, which get their name from their familiar chick-a-deee call, can now be heard singing their mating song, which sounds like “marry,” Holleback said.

Birds have calls, which they use to keep the flock together, and mating songs, she said.

Red-winged blackbirds returned a few weeks ago and crows are carrying sticks, another sure sign of spring, she said. Crows often use the same nest, relining it when needed.

Owls, the earliest nesters at Riveredge, already have their young, Holleback said.

“Great horned owls start nesting in January. The little ones hatch in February. They have two to three in a clutch,” she said.

“A year ago, some were nesting in a tall tree and a storm blew down the top part of the tree. We put a stand up in the tree, put the nest on the stand and they successfully fledged.”

Chipmunks have emerged from hibernation and are busy scampering for food and a mate.

Woodchucks, also called groundhogs, will awaken soon.

“We pull them out on Feb. 2 to forecast the winter, but they aren’t supposed to come out until late March,” Holleback said. “We haven’t seen them, yet. They respond to soil temperatures.”

But garter snakes have been seen slithering along the ground.

In the wetlands, skunk cabbage is emerging in dark purple pods and will soon form huge leaves that smell like a skunk when touched. The scent keeps the plant from being consumed by deer and other wildlife.

In the prairie, Holleback hunted for pasque flower, traditionally the first flower to bloom there. As its name suggests, the low plant with six to eight-inch stems and lavender flowers usually blooms at Easter time.

However, most spring flowers wait until Mother’s Day to bloom, Holleback said.

Young green hepatica leaves can be found among the old purple ones if debris covering the plant is pushed aside, but it will be a while before it blooms.

Pussy willows, which are only produced by female plants, are popping out.

Willow trees are turning a golden hue, red osier dogwood is a brighter red and bare-branched tamaracks, the only evergreen that loses its needles, will soon sport soft green fringe, Holleback noted.

Few people will get as excited as Holleback did when she spotted the first tiny strider fly skimming along the water as a stone fly emerged nearby. They look similar, but the strider fly spends its life in water, while the stone fly hatches in water but needs air to breathe, Holleback explained.

By April 1, the first swallows should return to Riveredge, Holleback said.

“I worry about them if it snows,” she said. “Robins can switch from berries to worms, but swallows are strictly insect eaters while on the wing.”